Search Results (290)

There is a knowledge gap about the effect of pharmaceutical agents on the biodegradation of Mg-based resorbable implants. The present work investigates how three common antibiotics and three anti-inflammatory drugs affect the corrosion of high-purity Mg, with and without ceramic and hybrid ceramic/polymeric coatings, using electrochemical impedance spectroscopy and hydrogen evolution tests. A Ca-P-Si-based ceramic coating is developed using plasma electrolytic oxidation (PEO), after the AC voltage and frequency parameters are optimized. A hybrid coating included a PEO and a poly(ε-caprolactone) (PCL) top layer formed by dip coating. High-purity Mg exhibited an instantaneous onset of corrosion with a corrosion rate of 90 μm/year after 24 h of immersion in a modified α-MEM. A hybrid PEO/PCL coating prevents the onset of corrosion for at least 5 h and reduces the H₂ evolution during the following 90 h by two times by the precipitation of 5–40 μm thick Ca-P surface deposits. Gentamicin, naproxen, streptomycin, ciprofloxacin and paracetamol were found to be corrosion accelerators with respect to bare h.p. Mg, whereas aspirin was found to be an inhibitor. Streptomycin-functionalized PEO/PCL system exhibited an active protection mechanism, triggered upon the release of the coating and substrate cations, associated with the coating defect-blocking action of the insoluble Me(II)-streptomycin chelates. Full article

Aluminum and its alloys are widely used in aerospace and industrial sectors due to their high specific strength, low density, and abundance. However, their low hardness, high corrosion susceptibility, and poor wear resistance limit broader applications. Surface treatments such as electroplating, PVD/CVD, and anodizing have been used to enhance surface properties. Plasma electrolytic oxidation (PEO), also known as micro-arc oxidation (MAO), has emerged as a promising technique for producing durable ceramic coatings on light metals like Al, Mg, and Ti alloys. In this study, PEO was applied to AA6061 aluminum alloy using an AC power source in potentiostatic mode at 350 V and 400 V, 1000 Hz, and 80% duty cycle for 30 min in a silicate-based electrolyte (5 g/L Na₂SiO₃ + 5 g/L KOH) maintained at 25–40 °C. The effect of voltage on the coating morphology, thickness, and corrosion resistance was investigated. The coatings exhibited porous structures with pancake-like, crater, and nodular features, and thicknesses ranged from 0.053 to 83.64 µm. XRD analysis confirmed the presence of Al, α-Al₂O₃, Ƴ-Al₂O₃, and mullite. The 400 V-coated sample showed superior corrosion resistance ( $E_{corr}= -0.77 \mathrm{V}$; $i_{corr}=0.28 \mu \mathrm{A}/{\mathrm{c}\mathrm{m}}^2$) and improved hardness (up to 233 HV), compared to 89 HV for the bare AA6061. Full article

This study investigates the influence of plasma electrolytic oxidation (PEO) on corrosion resistance of Ti6Al4V alloys produced by direct metal laser sintering (DMLS) for orthopedic implants. PEO (300 s) and flash-PEO (60 s) coatings containing Si, Ca, P, Mg and Zn were applied on both DMLS and wrought Ti6Al4V alloys. Samples, coated and uncoated, were characterized for microstructure, morphology and composition. Electrochemical behaviour was assessed by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF) at 37 °C. Ion release was quantified by inductively coupled plasma optical emission spectroscopy (ICP-OES). DMLS alloy was more passive than wrought Ti6Al4V, releasing ~60% less Ti and ~25% less Al, but ~900% more V. For both alloys, correlation of corrosion current and ion release indicated that 98–99% of oxidized Ti remained in the passive layer. Flash-PEO produced uniform porous coatings composed of anatase and rutile with ~50% amorphous phase, while PEO yielded heterogeneous layers due to soft sparking. In both cases, coatings were the main source of ions. For the DMLS alloy, the best protection was afforded by flash-PEO, releasing 0.01 μg cm⁻² d⁻¹ Ti, 26 μg cm⁻² d⁻¹ Al, and 0.25 μg cm⁻² d⁻¹ V over 30 days. Full article

Titanium alloys are widely employed in structural and electrochemical applications owing to their excellent mechanical properties and inherent corrosion resistance. However, their stability in harsh acidic environments, such as those encountered in energy storage systems, remains a critical issue. In this study, composite ceramic coatings were synthesized on a Ti6Al4V alloy using plasma electrolytic oxidation (PEO) in silicate-, phosphate-, and sulfate-based electrolytes, with and without the addition of α-alumina nanoparticles. The resulting coatings were comprehensively characterized to assess their surface morphology, chemical and phase compositions, and corrosion performance. Thus, the corrosion current density decreased from 9.7 × 10⁴ for bare Ti6Al4V to 143 nA/cm² for the coating fabricated in phosphate electrolyte with alumina nanoparticles, while the corrosion potential shifted anodically from –0.68 to +0.49 V vs. silver chloride electrode in 5 M H₂SO₄. Among the tested electrolytes, coatings produced in the phosphate-based electrolyte with Al₂O₃ showed the highest polarization resistance (113 kΩ·cm²), outperforming those fabricated in silicate- (71.6 kΩ·cm²) and sulfate-based (89.0 kΩ·cm²) systems. The composite coatings exhibited a multiphase structure with reduced surface porosity and the incorporation of crystalline oxide phases. Notably, titania–alumina nanoparticle composites demonstrated significantly enhanced corrosion resistance. These findings confirm that PEO-derived composite coatings provide an effective surface engineering strategy for enhancing the stability of the Ti6Al4V alloy in aggressive acidic environments relevant to advanced electrochemical systems. Full article

To explore the influence of the microstructure of plasma electrolytic oxidation (PEO) coating on the loading of corrosion inhibitors and the silanization treatment on its surface, PEO coatings were first prepared on the surface of AZ31B magnesium alloy under different voltages. Secondly, sodium tungstate (Na₂WO₄) was loaded into the micropores and onto the surface of the PEO coatings via vacuum impregnation, and which were subsequently subjected to silanization treatment. The phase composition of the coatings was studied by XRD, while the elemental composition and valence state were investigated by XPS. The surface and cross-sectional morphology of the coatings, as well as the composition and distribution of elements, were studied by SEM and EDS. Image J software was employed to analyze the thickness of the coatings. The results show that the microstructure of PEO coatings prepared under different voltages varies, which affects the loading of Na₂WO₄ on the surface of PEO coating and the sealing effect of silanization treatment, thereby influencing the corrosion resistance of the coatings. As the voltage increases, the coating thickness and roughness gradually increase, while the surface porosity first increases and then decreases, and the loaded content of Na₂WO₄ also follows a trend of first increasing and then decreasing. Meanwhile, at 300 V and 350 V, silanization treatment effectively seals the PEO coatings loaded with Na₂WO₄. However, when the voltage increases to 400 V, due to the uneven surface of the PEO coating, nonuniform distribution of micropores, and high roughness, the silanization treatment fails to completely cover the coating. This results in defects such as pits on the surface of the composite coating prepared at 400 V. Therefore, the composite coating prepared at 350 V exhibits the best corrosion resistance. After immersion in a 3.5 wt.% NaCl solution for 240 h, the composite coating formed at 350 V remains intact, and its low-frequency impedance modulus |Z|_0.01Hz is as high as 1.06 × 10⁶ cm². This value is approximately two orders of magnitude higher than that of the composite coating fabricated at 400 V and about three orders of magnitude higher than that of the pure PEO coating prepared at 350 V. Full article

Zinc-based alloys have been extensively studied for their potential applications in biodegradable materials, yet their corrosion behaviour necessitates the development of effective surface treatments. In this study, a ZnMg alloy was developed by casting in an inert medium and subsequently treating it with Plasma Electrolytic Oxidation (PEO). The corrosion behaviour was characterised in a 0.9% NaCl solution through Tafel polarisation, cyclic polarisation, and electrochemical impedance spectroscopy (EIS). Additionally, the surface morphology was investigated using scanning electron microscopy (SEM) and EDX analysis. The structure and phases of the oxide layer and of the corrosion products were investigated through X-ray diffraction (XRD). The electrochemical results demonstrated a substantial decrease in the corrosion current density and an increase in the polarisation resistance for the treated samples. Electrical Impedance Spectroscopy (EIS) modelling revealed the formation of a layer exhibiting distinct capacitive behaviour, comprising two distinct regions. XRD analysis confirmed evidence of corrosion compounds characteristic of chlorinated media on the surface. The findings indicated that PEO treatment enhanced the corrosion resistance of the ZnMg alloy, suggesting its suitability for biomedical applications or exposure to marine environments characterised by high levels of corrosion. Full article

In this work, a unique approach was used to synthesise black coatings on aluminium alloys (AA) 6061 and 7075 for applications in the aerospace field. In detail, plasma electrolytic oxidation (PEO) technology was used, maintaining the voltage constant at a relatively low value (V_max ≤ 292 V) during the process. NaVO₃ additive was used in the silicate-based electrolyte to obtain a black colour. The coatings were characterised by SEM-EDS, XPS, XRD, VIS-NIR spectroscopy, and EIS. The presence of vanadium oxides in the PEO coatings was detected by EDS, XPS, and XRD analyses. PEO coatings on AA7075 produced with 10 g/L of NaVO₃ exhibited exceptional optical characteristics, with a solar absorptance value of 95.3% in the VIS-NIR spectrum (wavelength range of 400–2000 nm). All the coatings improved the corrosion performances of the tested AA6061 and AA7075 by two or three orders of magnitude in 3.5 wt. % aqueous NaCl. Moreover, there was no sign of delamination, cracks, or any visible changes on coatings after thermal shock, performed by cycling samples between two extreme temperatures, −196 °C and 150 °C, respectively. Full article

This study explores the influence of significant manufacturing parameters, i.e., peak current density and frequency, on the oxide coatings’ micromechanical and sclerometric properties. The parameter levels were determined using a full experimental design with two variables at three levels. Plasma electrolytic oxidation (PEO) was conducted on an ultralight LA141 magnesium alloy in an alkaline ternary electrolyte. Coating performance was characterized by measuring hardness (HIT) and Young’s modulus (EIT), as well as three loads significant to coating failure: L_c1, the initiation of Hertzian tensile cracks; L_c2, the initiation of cohesive coating failure; and L_c3, full delamination of the coating. Scratch testing was complemented by profilographic analysis to provide isometric surface images. Statistical analysis was then employed to ascertain correlations of process parameters with the developed mechanical and sclerometric properties. Full article

The use of biomedical implants has significantly enhanced patient survival rates and overall quality of life. However, bacterial infections caused by bacterial adhesion and the subsequent formation of biofilm on the surface of the implants are challenging clinical issues, leading to implant failure and high social and economic costs. Modification of the surface of the implants with antibacterial coatings is a promising technique to address implant-associated bacterial infection problems. One strategy to fabricate bactericidal antibacterial coatings is to load antibacterial agents, like antibiotics—the most important type of antibacterial drug for killing or inhibiting the growth of bacteria—at therapeutic doses into the coatings and subsequently release them, ideally in a controlled way. Plasma electrolytic oxidation (PEO) is a simple, affordable, and eco-friendly method to produce high-performance, multifunctional coatings with desired antibacterial properties. This review examines the antibacterial activity of antibiotic-loaded PEO coatings, offering valuable insights for the development of novel, high-performance antibacterial coatings that meet clinical requirements. Full article

Titanium alloys are frequently subjected to surface treatments to enhance their biocompatibility and corrosion resistance in biological environments. Plasma electrolytic oxidation (PEO) is an environmentally friendly electrochemical technique capable of forming oxide layers characterized by high corrosion resistance, biocompatibility, and strong adhesion to the substrate. In this study, the PEO process was performed using a low-melting-point ternary eutectic electrolyte composed of Ca(NO₃)₂–NaNO₃–KNO₃ (41–17–42 wt.%) with the addition of ammonium dihydrogen phosphate (ADP). The use of this electrolyte system enables a reduction in the operating temperature from 280 to 160 °C. The effects of applied voltage from 200 to 400V, current frequency from 50 to 1000 Hz, and ADP concentrations of 0.1, 0.5, 1, 2, and 5 wt.% on the growth of titanium oxide composite coatings on a Ti-6Al-4V substrate were investigated. The incorporation of Ca and P was confirmed by phase and chemical composition analysis, while scanning electron microscopy (SEM) revealed a porous surface morphology typical of PEO coatings. Corrosion resistance in Hank’s solution, evaluated via Tafel plot fitting of potentiodynamic polarization curves, demonstrated a substantial improvement in electrochemical performance of the PEO-treated samples. The corrosion current decreased from 552 to 219 nA/cm², and the corrosion potential shifted from −102 to 793 mV vs. the Reference Hydrogen Electrode (RHE) compared to the uncoated alloy. These findings indicate optimal PEO processing parameters for producing composite oxide coatings on Ti-6Al-4V alloy surfaces with enhanced corrosion resistance and potential bioactivity, which are attributed to the incorporation of Ca and P into the coating structure. Full article

This work aims to clarify whether the individual advantages of the two commonly used silicate- and aluminate-based electrolytes for the plasma electrolytic oxidation (PEO) of steel can be combined in a two-step process. The first PEO step was carried out in an aluminate–phosphate electrolyte with pulsed voltage and anodic amplitudes between 150 V and 200 V. The second PEO step was carried out at an increased anodic voltage amplitude of 400 V in a silicate–phosphate electrolyte. As a reference, PEO was conducted in a single step in the same silicate–phosphate electrolyte at an increased anodic voltage amplitude of up to 400 V. The microstructural layer analysis was carried out using SEM and EDX analyses, Raman spectroscopy and XRD analysis. Heterogeneous layers containing iron oxide and iron phosphate form in the silicate–phosphate electrolyte at anodic voltage amplitudes up to 300 V by electrochemical reactions. Further increasing the anodic voltage amplitude up to 400 V results in heterogeneous layers, too. PEO in the aluminate–phosphate electrolyte at 150 V causes the formation of thin, amorphous layers mainly consisting of aluminum and iron oxides. At 200 V amplitude, a PEO layer with pronounced open porosity is formed, which primarily consists of the crystalline phases corundum and hercynite. During subsequent PEO in the silicate–phosphate electrolyte, the previously formed layers were replaced by a macroscopically homogeneous layer that is mostly nanocrystalline and may contain amorphous iron(-aluminum) phosphates and oxides as well as silicon oxide. It can be concluded that the two-step PEO process is suitable for the production of more homogeneous PEO layers. Full article

Plasma electrolytic oxidation (PEO) is an advanced electrochemical surface treatment technology. It can effectively improve the corrosion resistance of magnesium and its alloys. This paper aims to form protective PEO coatings on an AZ31 substrate with different electrolytes, while monitoring the micro-discharge evolution by noise intensity and morphology analysis. By setting the PEO parameters and monitoring process characteristics, such as current density, spark appearance, and noise intensity, it was deduced that the PEO process consists of the following three stages: anodic oxidation, spark discharge, and micro-arc discharge. The PEO oxide coating formed on the AZ31 alloy exhibits various irregular volcano-like structures. Oxygen species are uniformly distributed along the coating cross-section. Phosphorus species tend to be enriched inwards to the coating/magnesium substrate interface, while aluminum piles up towards the surface region. Surface roughness of the PEO coating formed in the silicate-based electrolyte was the lowest in an arithmetic average height (Sa) of 0.76 μm. Electrochemical analysis indicated that the corrosion current density of the PEO coating decreased by about two orders of magnitude compared to that of untreated blank AZ31 substrate, while, at the same time, the open-circuit potential shifted significantly to the positive direction. The corrosion current density of the 10 min/400 V coating was 1.415 × 10⁻⁶ A/cm², approximately 17% lower than that of the 2 min/400 V coating (1.738 × 10⁻⁶ A/cm²). For a fixed 10 min treatment, the longer the PEO duration time, the lower the corrosion current density. Finally, the tested potentiodynamic polarization curve reveals the impact of different types of PEO electrolytes and different durations of PEO treatment on the corrosion resistance of the oxide coating surface. Full article

The friction surfacing (FS) process has emerged over the past few years as a method for joining both similar and dissimilar materials, for volume damage repair of defective components, and for corrosion protection. The possibility to produce a metallic coating by FS, without melting the material, classifies this technique as distinct from other standard methods. This unconventional deposition method is based on the severe plastic deformation that appears on a rotating metallic rod (consumable material) pressed against the substrate under an axial load. The present study aims to investigate the tribological properties and corrosion resistance provided by the aluminum-based FS coatings deposited onto a structural S235 steel substrate and further modified by plasma electrolytic oxidation (PEO). During the PEO treatment, the formation of a ceramic film is enabled, while the hardness, chemical stability, corrosion, and wear resistance of the modified surfaces are considerably increased. The morpho-structural characteristics and chemical composition of the PEO-modified FS coatings are further investigated using scanning electron microscopy combined with energy dispersive spectroscopy analysis and X-ray diffraction. Dry sliding wear testing of the PEO-modified aluminum-based coatings was carried out using a ball-on-disc configuration, while the corrosion resistance was electrochemically evaluated in a 3.5 wt.% NaCl solution. The corrosion rates of the aluminum-based coatings decreased significantly when the PEO treatment was applied, while the wear rate was substantially reduced compared to the untreated aluminum-based coating and steel substrate, respectively. Full article

This study presents the development and comprehensive evaluation of magnesium-based implants with surface modifications using selected polymers and bioactive compounds. The implants were fabricated via plasma electrolytic oxidation (PEO), followed by the application of chitosan, polydopamine (PDA), and gold nanoparticles as bioactive surface coatings. In vitro experiments, including FT-IR spectroscopy, scanning electron microscopy (SEM), wettability tests, biodegradation assays in simulated body fluid (SBF), electrochemical corrosion analysis, and cytotoxicity tests using MG-63 osteoblast-like cells, were employed to assess the physicochemical and biological properties of the materials. The PEO + PDA-modified samples demonstrated the highest corrosion resistance (−1.15 V corrosion potential), enhanced cell viability (~95%), and favorable surface wettability (contact angle ~12.5°), outperforming other tested configurations. These findings suggest that PEO combined with PDA offers a synergistic effect, leading to superior biocompatibility and degradation control compared to unmodified magnesium or single-coating strategies. The developed implants hold promise for orthopedic applications requiring biodegradable, bioactive, and cytocompatible materials. Full article

A plasma electrolytic oxidation (PEO) coating was produced on 6061 aluminum alloy within a silicate-containing electrolyte using a bipolar pulsed power supply. The impact of K₂ZrF₆ addition on the wear resistance of the coating was investigated. The phase composition, surface morphology, and elemental distribution of the coatings were assessed by means of X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and scanning electron microscopy (SEM). Experimental data revealed that the growth rate of the coating increased by 37.3% compared to that without K₂ZrF₆; the addition of K₂ZrF₆ favored the formation of mullite and enhanced the coating densification; it also improved the breakdown voltage of the coating, which increased by 46.0% compared to that without K₂ZrF₆; and it also demonstrated excellent abrasion resistance, with a reduction of 41.8% in the weight of the abrasion. Full article